Typically the hot incandescent coke that has been pushed from a coking oven is collected in a quench car mounted on rails for transportation into the quenching chamber located in the base of a quenching tower. It is the general practice to shower the incandescent coke while contained in the quench car with large volumes of water in the form of a spray for about one to three minutes. After quenching, the car is withdrawn from the quenching tower to deliver and discharge the coke at a coke wharf.
The quenching tower customarily has an entranceway or opening in its base to permit passage of the quench car into and, in some cases, completely through the quenching chamber of the tower. When the incandescent coke retained in the cars is sprayed with water, emissions are generated which principally comprise steam containing entrained particulate matter and water droplets. These hot emissions, which ascend into the stack of the quenching tower to exhaust from the top opening, create a drafting effect that causes large volumes of air to flow into the base of the tower through the entranceways for the quench car. Upon entering the quenching chamber, these infiltrating volumes of air are heated by mixing with the hot emissions and flow quickly up and out the stack, thus enhancing the drafting effect. Moreover, the large volumes of infiltrating air greatly increase the quantity of gaseous emissions that need to be cleaned to meet increasingly stringent air pollution limitations. Tests have shown that quenching tower emissions are only 25 to 35% water vapor with the remaining 65 to 75% comprising air. This large percentage volume of air makes the quenching emissions more dilute and thus harder to clean. It also increases the gas velocity up the stack of the quenching tower, thus entraining more particulates and water droplets in the exhaust stream than would otherwise occur.
It is known in the art to control the discharge into the atmosphere of solid particles and droplets of water that are entrained in the rapidly flowing gaseous emissions by the use of clean water sprays and baffles, or mist eliminators, in the stack of the tower. However, these baffles are only effective in capturing the larger water droplets and particulates.
Numerous attempts have been made by workers in the art to reduce the volume or control the flow of quenching emissions. U.S. Pat. No. 2,975,106 to Becker provides a quenching tower with doors for completely closing off the passageways of the quench chamber to prevent the infiltration of air and reduce the volume of emissions that have to be cleaned by water sprays and baffles in the tower. U.S. Pat. No. 3,684,664 to Stratmann et al discloses another means for sealing a quench chamber from the outside air comprising a quench chamber having an entranceway or a complete tunnel-like passage for a quench car formed in the precise outline of the car. U.S. Pat. No. 3,806,032 to Pries shows adjustable louver-like closure means in the upper part of the tower to control the passage of the rising air currents and steam.
It is standard practice in the art to collect the water used in the quenching operation in a water sump for recycling. Fresh make-up water is added as necessary. Water from the water sump is supplied to the sprays in the quenching tower where a portion of the sprayed water vaporizes into steam and the remainder returns to the sump after having been warmed during the quenching process. Accordingly, the sensible heat content of this recirculated water quickly rises to the point where the sensible heat extracted from the incandescent coke during the quenching process is transformed into the latent heat of vaporization of the quench water. In this manner substantially all of the sensible heat lost by the hot coke results in the generation of volumes of steam rather than merely increasing the temperature of the quench water.
There is a need for a more effective control of quenching emissions by reducing the quantity of gas moving through the quenching tower.
There is also a need to reduce gas velocity through the quenching tower in order to reduce the entrainment of particulate matter and water droplets in the emissions.
Further there is a need to concentrate the quenching emissions so that clean water sprays can more effectively clean the emissions as well as cool the emissions to condense water vapor within the quenching tower.